1. Field of Invention
This invention generally relates to self loading firearms, specifically to gas blocks for self loading firearms which facilitate user adjustment of the gas output. The Switchblock is designed to regulate the flow of propellant gasses which are used to cycle the self loading mechanism of the firearm. The preferred embodiment of the invention is for use with an AR15/M16 type rifle but this should not be seen as a limitation on the technologies application to other firearms.
2. Prior Art
Adjustable gas blocks have been used on autoloading rifles since WWII. Rifles such as the Soviet SVD, Yugoslavia's M76, Belgium's FAL, AR10 SASS rifle, and the recent Belgium SCAR rifles all incorporate adjustable gas blocks. What has changed is the purpose behind the incorporation of an adjustable gas block.
Gas blocks for autoloading firearms have traditionally been used as a means to collect, restrict, and direct the flow of gas from the firearm barrel and into the autoloading rifle's gas system. Early adjustable gas blocks were an attempt to minimize the wear of the host firearm by placing the minimal amount of gas necessary to properly operate the firearm into the operating system. Another common reason was for rifle mounted grenades, which required special cartridges to fire properly.
Modern adjustable gas block designs such as are present on the ArmaLite AR10 SASS and SCAR rifles are utilizing adjustable gas blocks as a means to restrict the increased flow of gas to the operating system which is the result of using a silencer.
Silencers increase the amount of gas forced through the gas system by a phenomenon known as back pressure. The addition of more gas into the operating system causes increased fouling of the weapon mechanical components, a variety of operation related malfunctions, and place unnecessary wear on the firearms internal components.
In the past designs such as the Belgium FAL have incorporated gas blocks which offer multiple settings whereby the amount of gas directed into the firearm is variable by toggling a switch. The flow of gas allowed to pass from the barrel into the operating system was either on or off. This design also has a threadedly secured nut which partially blocked a gas port on the gas system which could be actuated to further increase or decrease the flow of gas. The intent of this design was to allow the user to regulate the amount of gas allowed into the operating system based on ammunition used and barrel length.
Systems such as this present several problems. The FAL gas blocks' primary method of regulating gas flow is by venting gas into the atmosphere above the gas system. When combusting powder hits the oxygen rich environment it creates flash and noise. This precludes such a system from use with a silencer because flash and noise reduction are the primary functions of a silencer. Another disadvantage is the difficulty of adjustment. Adjusting the gas flow requires a wrench and offers a variety of settings none of which are pre set. This makes the system impractical for field expedient adjustments.
Other designs such as the ArmaLite AR10 gas block offer the user an ability to regulate the flow of gas by toggling a screw which occludes the port which allows gas to flow into the gas block and subsequently into the gas system. This system was purposed designed for use with a silencer and offer two positions of operation. Standard gas flow and a reduced gas flow are the only two options afforded the user.
Design such as present on ArmaLite's AR10 SASS rifle only offer two adjustments position, one which is standard flow another which is a reduced flow. Further, no provision to prevent gases from escaping from the gas block and generating flash and sound are provided for.
The present invention offers several advantages over the prior art. Three positions of adjustment are afforded the user. Standard gas flow, reduced gas flow, and no gas flow. The no gas flow allows the user to stop the autoloading capability of the host firearm and to maximize both the accuracy of the firearm and the sound reduction capability of the silencer. A spring loaded detent is utilized to hold the gas regulator knob in each position and allows for quick, field expedient adjustment. This system works by restricting the flow of gas from the host firearm barrels gas port, and not by venting the excess gas into the atmosphere. Further, gas rings are utilized within the housing to prevent the pressurized gases from escaping. The amount of gas necessary to operate the rifle on both the standard and reduced gas flow settings is determined at the factory based on the caliber, barrel length, and gas system length of the host firearm. When a gas block, which embodies the present invention, is installed a gas tube is also incorporated which has apertures that determine the amount of gas allowed to pass into the operating system.